The current state of the art provides different gas heating devices to be used in several applications, such as those which promote heat exchange by convection, that is, those in which the gas heating device is submerged in the bath of the liquid or viscous fluid to be heated, such as the thermal baths in the equipment designed to be used for frying or heating food.
In a summarized manner, these gas heating devices comprise a gas inlet chamber provided with gas injection nozzles, which are directed so as to produce, upon gas burning, respective flows of combustion gases through the interior of the heat tubes or heat propagation tubes. The heat, generated by the burning of the gas released by the injection nozzles, passes, with reduced speed through the interior of the heat tubes, which are usually provided submerged in the bath of the fluid to be heated.
The gas heating devices of the type described above allow the fluid (liquid or viscous) to be heated, without direct contact with the gas, with the flames resulting from gas burning, and with the combustion gases. Despite presenting these positive aspects, said usual gas heating systems tend to present low efficiency, besides usually promoting unequal heating of the fluid mass to be heated.
The low heating efficiency of the fluid mass is related to different factors, among which it may be cited the gas pressure to be released by the gas injection nozzles, it being however observed that the smaller the gas pressure, the less the thermal efficiency of the system.
Another factor that may cause a low thermal efficiency is related to the unequal heating of the fluid mass, due to the behavior of the flow of the combustion gases which is passed through the heat exchange tube maintained immersed in the fluid mass to be heated.
The usual heat tubes present a geometry defined by a continuous or substantially continuous cross section, which is devoid of elements for controlling the flow of the combustion gases. Thus, the thermal energy contained in the combustion gases produced by the burning of the gas that is released, usually at high pressure, by the gas injection nozzles, tends to be transmitted to the walls of the heat exchange tube in a non-homogeneous manner, provoking an unequal heat transmission to the fluid mass to be heated, and thus impairing an homogeneous heating of the fluid mass to be obtained with an efficiently acceptable gas consumption.
Considering the above mentioned drawbacks related to the usual gas heating devices, it was proposed the gas heating device described and claimed in Brazilian patent application MU8901837-0 of the same applicant. In this previous construction, each gas heating device comprises a gas inlet chamber provided with two parallel alignments of gas injection nozzles, the axis of each one of the nozzles of one alignment being horizontally coplanar and convergent in relation to the axis of a respective nozzle of the other alignment. The injection nozzles are provided with a radial primary air inlet, whereby the combustible flow, released by the injection nozzles, becomes a mixture of air and gas to be burned in the inlet of a respective heat exchange tube, to be maintained submerged in the fluid mass to be heated, usually contained in a tank. This constructive arrangement makes the flows of the combustion gases, coming from each two opposite and horizontally coplanar injection nozzles, to be fed in a convergent manner, to an inlet end of the heat propagation tube, said flows being mixed, in a somewhat turbulent manner, with the secondary atmosphere air, being then burned and displaced through the interior of the heat exchange tube, until reaching the outlet of the latter. The release of the gas by the gas injection nozzles should be made at a high pressure in order to obtain an efficient burning.
Aiming at maintaining the flows of the combustion gases produced by each two coplanar injection nozzles, suitably distributed throughout the entire height of the heat exchange tube and longitudinally displaced in the latter at a thermally efficient speed, the heat propagation tube of said previous construction is internally divided, throughout its height, in multiple ducts, each being operatively related to a pair of coplanar gas injection nozzles and being medianly and longitudinally provided with a deflecting wall formed in alternately inclined segments and provided with slots or windows for the controlled passage of the combustion gases along the respective duct.
Although allowing a homogeneous distribution of the flow of the combustion gases, in their displacement through the heat exchange tube, and also a controlled displacement speed of the combustion gases, the solution, object of said MU8901837-0, presents an excessively complex and costly construction, requiring a gas feed at high pressure and the provision of a great number of gas injection nozzles arranged to operate in pairs and constructed with a primary air inlet, in order to allow the formation of flame, upon releasing the combustible mixture through the gas injection nozzles in the inlet region of the heat propagation tube. Further, it is required the provision of a structure of complex construction to be mounted in the interior of the heat exchange tube, in order to form the longitudinal ducts and their respective perforated deflecting walls. Without said ducts, neither the desired homogenous heat distribution throughout the whole height of the heat exchange tube, nor a thermally efficient speed of the combustion gases during the passage thereof through the ducts are obtained.